Common converters
Speed Converter
Convert mph, km/h, m/s, knots and other speed units.
Result
0.621371 mph
1 km/h = 0.621371 mph
All units for this value
| Unit | Symbol | Value |
|---|---|---|
| Millimeter per second | mm/s | 277.778 |
| Centimeter per second | cm/s | 27.7778 |
| Meter per second | m/s | 0.277778 |
| Kilometer per hour | km/h | 1 |
| Kilometer per second | km/s | 0.000277778 |
| Foot per second | ft/s | 0.911344 |
| Mile per hour | mph | 0.621371 |
| Mile per second | mi/s | 0.000172603 |
| Knot | kn | 0.539957 |
| Mach (sea level, 15 °C) | Ma | 0.000816297 |
| Speed of light | c | 9.26567e-10 |
About this calculator
Speed describes how fast something moves, expressed as distance covered per unit of time. This converter switches between everyday units like kilometres per hour and miles per hour and more specialized ones like knots and Mach, so you can compare readings from cars, planes, boats, and weather reports on the same scale.
How it works in plain English
Every speed unit is really a ratio of a distance unit to a time unit, so converting between them means rescaling both parts at once. The converter treats metres per second as the common anchor: it multiplies or divides your entered value by a fixed factor to reach that anchor, then applies a second factor to reach whichever unit you asked for. This two-step path keeps the math consistent no matter which pair of units you pick.
Some units carry extra context. A knot is a nautical mile per hour, used at sea and in aviation. Mach compares a speed to the local speed of sound, which itself depends on air temperature and altitude, so the converter uses the standard sea-level value for that comparison. The speed of light is a fixed physical constant, useful mainly as a reference point rather than something you'd measure directly.
Pick your starting unit and the unit you want in the from and to menus, type a number, and the result updates immediately. A full table lists the same value in every supported unit at once, and a precision control lets you show more or fewer decimal places. A swap button flips the two chosen units in one click.
The formula
- value_in_target = value_in_source × (source factor to m/s) ÷ (target factor to m/s)
- 1 mph = 0.44704 m/s
- 1 km/h = 1 ÷ 3.6 m/s
- 1 knot = 1852 ÷ 3600 m/s = 0.514444 m/s
- 1 ft/s = 0.3048 m/s
- Mach 1 (sea level, 15 °C) ≈ 340.29 m/s
- c = 299,792,458 m/s
Worked example
Say a car's speedometer reads 100 km/h and you want to know that in miles per hour. First convert to the common anchor, metres per second: 100 km/h × (1 ÷ 3.6) = 27.78 m/s. Then convert from metres per second into miles per hour by dividing by the mph factor: 27.78 ÷ 0.44704 = 62.14 mph.
The converter performs both steps behind the scenes the instant you type 100 into the km/h field with mph selected as the target, showing 62.14 mph right away. Checking the full unit table at the same time also shows this equals about 27.78 m/s, 91.13 ft/s, and 0.0518 knots, all from a single entry.
Common speed unit equivalents
| Unit | Equal to (m/s) |
|---|---|
| 1 m/s | 1 |
| 1 km/h | 0.277778 |
| 1 mph | 0.44704 |
| 1 ft/s | 0.3048 |
| 1 knot | 0.514444 |
| Mach 1 (sea level) | 340.29 |
| Speed of light (c) | 299,792,458 |
Standard unit definitions
Frequently asked questions
Why isn't Mach a fixed number of metres per second?
The speed of sound changes with air temperature, pressure, and altitude, so Mach 1 is faster near the ground on a hot day than high in cold thin air. This converter uses the widely quoted sea-level, 15 °C reference value of about 340.29 m/s, which is standard for general comparisons but not exact for every altitude.
What's the difference between a knot and a mile per hour?
A knot is one nautical mile per hour, and a nautical mile (1852 metres) is slightly longer than a statute mile (1609.344 metres) used in mph. Because of that, one knot equals about 1.15 mph, not exactly one. Knots are the standard unit in marine and aviation navigation.
How precise are the converted results?
Conversions use exact defined factors, such as 0.44704 for mph, so results are as precise as the number of decimal places you choose to display. You can widen or narrow the precision setting to show more or fewer digits, which is useful when comparing very close speeds or rounding for a simple readout.
Can I convert several speeds at once?
Yes. Once you type a value into the from field, the results table shows that same speed already converted into every other supported unit simultaneously, so there's no need to repeat the calculation one unit at a time.
Why does the speed of light matter here?
It's included mainly as a reference constant rather than a practical everyday speed. Seeing how a car's or plane's speed compares as a tiny fraction of light speed can help put physics discussions or curiosity questions into perspective, using the exact defined value of 299,792,458 metres per second.
Calculators that use these units
- Pace Calculator — Solve for pace, time, or distance and predict race times.
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